WO1994004089A1

WO1994004089A1 - Improvements in dental crowns

Info

Publication number: WO1994004089A1
Application number: PCT/AU1992/000431
Authority: WO
Inventors: John Fung
Original assignee: John Fung
Priority date: 1992-08-14
Filing date: 1992-08-14
Publication date: 1994-03-03
Also published as: AU2476892A

Abstract

A dental prosthesis (6) comprises an outer shell-like body (4) of fully fired porcelain material into the cavity of which is placed porcelain powder (5); that porcelain powder (5) being partially fired so as to remain coherent when the prosthesis (6) is pushed over a tooth preparation (1) to mould the porcelain powder to the shape of that tooth preparation. After the fitting process the prosthesis (6) is fired to complete firing of the now shaped porcelain powder (5) before final fitting of the prosthesis (6) to the tooth preparation.

Description

"IMPROVEMENTS TN DENTAL CROWNS" Field of the Invention

The present invention relates to the construction of a dental prosthesis and more particularly a prosthesis in the form of a crown, inlay, facing or similar structure being an advance upon the structure as disclosed in my international patent application PCT/AU91/00300, the contents of which are incorporated herein by reference.

Prior Art In my earlier application as referenced above a dental prosthesis was formed by positioning and bonding an insert into the cavity of a dental outer body shell prior to fitment of the combined insert and body shell to a prepared tooth remnant. Description of Invention

In contrast the present invention proposes a dental prosthesis (defined herein as a crown, inlay, facing or the like) comprising an outer body functionable as a tooth or part thereof, which outer body has been finally formed and cured with the outer appearance of at least a part of a tooth in the form of a partial shell-like body, said outer body being at least in part filled with partially fired porcelain powder.

The fitting of a prosthesis of this invention is achieved by wetting of the partially fired porcelain powder within the shell before pushing the shell containing the partially fired porcelain powder over a partially flexible, textured covering over a tooth preparation, whereafter the outer body and its contained partially fired porcelain powder filling is removed from the tooth preparation and fully fired prior to fixing the outer body and its contained fully fired porcelain over the insert on the tooth preparation. By means of the present invention there is provided an easy technique for precisely fitting a dental prosthesis which uniquely matches a tooth preparation.

By having the outside layer or shell of the prosthesis harder than the inside partially fired porcelain it is a ready procedure to fit the prosthesis over a prepared tooth to take the shape of the post of the tooth or more particularly a stainless steel mesh fitted over the post.

Because the filling of the shell like prosthesis is partially fired before fitment over the post it tends to retain its shape when wetted and fitted over the post in contrast with totally unfired porcelain powder which lacks stability and tends to separate from the shell like outer part of the prosthesis if employed during the fitting phase of the prosthesis to the tooth preparation. It is preferred that the insert is stainless steel mesh, or other corrosion resistant tensile material mesh.

The mesh supports the porcelain as well as provides a strong mechanical interlocking of the porcelain to the mesh by way of the oxide bonding material. The completed prosthesis device may be bonded to a prepared tooth remnant using dental cement, filling material or adhesive.

The prosthesis may be in a number of forms including a full crown, an inlay, a cosmetic facing, or an integral tip and facing.

In another broad form the invention can be described as a method of manufacturing a dental prosthesis comprising: forming an outer shell-like body functionable as a tooth or part thereof, which outer body has been finally formed and cured with the outer appearance of at least a part of a tooth, said body being at least in part filled with porcelain powder and partially fired.

The body may be a heat fusible porcelain. The insert may be stainless steel mesh. In an alternative procedure, a dental surgery is supplied with a range of sizes of fully formed shell-like crowns, or the like, from which an appropriate size is selected to suit the remaining teeth. The mesh will be sized according to the tooth size so as to ensure adequate strength, and the tooth remnant is prepared to be just slightly smaller than the mesh. The selected crown is partially filled with porcelain powder and partially fired. The partially fired porcelain powder in the crown is wetted and the crown is press-fit over the mesh covered remnant. Once the fitted crown is removed from the mesh covered remnant, it is fired with or without the mesh in situ within the partially fired porcelain of the crown before finally adhering the crown to the tooth remnant. Description of Drawings

By way of example only an embodiment of the invention will be described with reference to the accompanying drawings, in which:-

Fig. 1 is a sketch of a disassembled prosthetic crown remnant in accordance with the present invention;

Fig. 2 shows a sectional view of a stage in the formation of unique fitment of the crown of Fig. 1 over the prepared tooth and mesh; and

Fig. 3 shows a sectional view of a crown removed from a prepared tooth and covering mesh prior to final firing and before fixing of the finally fired crown to the prepared tooth and mesh. Description of Preferred Embodiments

Fig. 1 shows a tooth preparation 1 in the patient's jaw 2, the post having already been prepared by conventional dental grinding techniques to form a strong, healthy post to which the crown may be attached.

A porcelain crown 4 is shaped so as to simulate the function and appearance of a natural tooth in a healthy condition. Within crown 4 is partially fired porcelain powder 5. Intermediate the post 1 and the crown 4 is a stainless steel mesh skeleton 3 which is bonded in a mechanically interlocking manner by virtue of its mesh structure, to the porcelain powder 5 inside the cavity of the crown 4. The complete crown 6, incorporating the stainless steel mesh 3, fired porcelain powder 5, and the porcelain crown 4, is adhered to the post 1 by using conventional dental cement, filling material or adhesive. The flexibility of the stainless steel (or other suitable material) mesh 3 provides a complete crown structure 6 which has much more give than does a crown produced by conventional techniques. Thus, crown 6 is much less likely to failure. Moreover, because the texture of the mesh provides an interlocking bond with the porcelain filling 5 of shell-like crown 4, if damage does occur to the porcelain it will tend to remain wholly fixed in place rather than fragment and become loose in the patient's mouth.

The relative thinness of the stainless steel mesh 3 allows a relatively thick body of porcelain in the crown 4 and filling 5 and thus provides very good aesthetic qualities which are much closer to those of natural teeth than is the case of traditional crowns formed on solid metal cores. Also to improve aesthetics, the porcelain material may be specified such as an outer enamel porcelain layer, intermediate dentine porcelain layer, and inner opaque porcelain encasing the mesh 3.

The completed crown 6 can be formed and fitted in any one of a variety of procedures. Standard porcelain shells 4 can be produced in varying sizes and shapes and partially filled with partially fired porcelain powder 5 and kept on hand in the dental surgery. The stainless steel mesh 3 is shaped to suit a prepared tooth preparation 1, and then inserted into a suitable pre-made crown 4 containing powder 5 before removal and baking. This baking and finishing procedure will likely require only approximately one hour and then the mating crown can be bonded to the mesh 3 and tooth preparation 1 using dental cement. Thus a high quality, permanent crown can be fitted in a single visit to the dental surgery.

In a particularly time efficient procedure, completed, fully fired crowns 4 containing partially fired porcelain powder 5 are produced in a dental laboratory in a variety of sizes for each tooth type. The mesh 3 for the crowns 4 will be sized according to the outer size of the crown 4 so as to ensure sufficient porcelain thickness for strength, but with as large as possible inner cavity so as to allow fitment to as large as possible tooth remnant 1. In the surgery the dentist selects the appropriately sized crown 4 and prepares the remnant 1 to the appropriate size. The partially fired porcelain powder 5 is wetted and the crown 4 pressed over mesh 3 on post 1. After removal of the crown 4 it is fully fired to fix the shape of the powder 5 to that of the mesh 3 on post l before final fixing to post 1 via intermediate mesh 3.

A filler material is plastic, or paste like, and fills in any space between the mesh 3 and the remnant 1. The filler material cures, normally in about 5 minutes and the job is complete.

Thus the patient may select to have a custom shaped crown in order to best duplicate the true shape of the natural tooth being repaired or a cheaper but equally strong alternative. In all cases the crown may be mechanically superior to previously known crowns.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS :

1. A dental prosthesis comprising an outer body functionable as a tooth or part thereof, which outer body has been finally formed and cured with the outer appearance of at least a part of a tooth in the form of a partial shell-like body, said outer body being at least in part filled with partially fired porcelain powder.

2. A dental prosthesis as claimed in claim 1 wherein said outer body is of porcelain or the like which has been heat hardened.

3. A method of manufacturing a dental prosthesis comprising: forming an outer shell-like body functionable as a tooth or part thereof, which outer body has been finally formed and cured with the outer appearance of at least a part of a tooth, said body being at least in part filled with porcelain powder and partially fired.

4. A method as claimed in claim 3 comprising bonding a shaped textured corrosion resistant flexible insert into the porcelain powder.

5. A method as claimed in claim 4 wherein the bonding is effected after the porelain powder has been fully fired.

6. A method as claimed in claim 4 wherein the bonding is effected before or during final firing of the porcelain powder.

7. A method as claimed in any one of claims 4-6 wherein the insert is a mesh comprised of a woven tensile filament material.

8. A method as claimed in claim 7 wherein the filament material is corrosion resistant metal or wire.

9. A method as claimed in any one of claims 4-8 wherein the insert is firstly shaped about a tooth remnant, or a casting of a tooth remnant and removed from said remnant or casting before positioning said insert into the partially fired porcelain powder within the outer body to the shape of the remnant when covered by the insert.